Variable inductance



Feb. 171, 1947. R. F, J, FLOOD EI-AL 2,415,736

VARIABLE INDUCTANCES Filed April 22, 1943 Snnentorls EGINHLD EJ. FL Bv EGINHLD C.\/|NE El 2g. Gttorneg "llllllll T.

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Patented Feb. 1l, 1947 VARLCBLE INDUCTANCE Eegina-ld Francis Joseph Flood and Reginald ROIS Vine, Sydney, New South Wailea Australia, to fimalgamated VJircless 'fr asia) Limited, Sydney, New South Wales, Australia, a company of Neuv South Wales Application April 22, 1943, Serial No.

(Ausln Australia May 19, 1942 (Cl. Vil- 242) 4 Claims. 1

This invention relates to continuously variable inductances and in particular to variable inductanoes for use in the or frequency determin ing circuits of radio transmitters and similar equipment.

The present invention is specically applicable for use with variable inductances of the type described and claimed in Australian Patent No. 108,553 which discloses a continuously variable device comprising a helical coil having an axis of rotation, an electrically conducting rod mounted parallel to said a-Xis, a rotatable metal Wheel slidably carried by sai@` rod in Contact with said coil, means for rotating said coil to vary the Contact position of said Wheel whereby the effecu tive inductance value of said coil is altered.

The coil mentioned usually consists of a helix of metal ribbon wound edge-wise on a form which supports the turns of the helical Winding in spaced relation While the rotatable Contact wheel is in the form of a grooved pulley spring urged towards said Winding. Alternatively the conducting rod, on which said rotatable Wheel is slidably mounted, is resiliently biased towards the axis of rotation of said coil to maintain said wheel in contact With said coil.

In operation it has been found that when the effective inductance of said coil has been adjusted to or near its minimum value, the major portion of said coil, although short circuited to ground or equivalent potential via the abcvementioned contact Wheel, resonates at a frequency within the range covered by the eective portion of said coil, thereby absorbing useful energy from the effective portion of the circuit in use.

It is therefore the object of the present invention to provide means whereby this undesired or reactionary resonance characteristic, in the shortcircuited portion of the coil, is broken into components of resonance that do not appreciably interfere with or counteract the primary or useful resonance characteristic in the effective portion of the coil.

According to this invention the above speoied desideratum is attained by a means adapted to automatically connect a point of said coil to ground, intermediate of the portion short-cir cuited to ground by said contact Wheel, when the latter has been moved to reduce the effective inductance value of said coil by a substantial amount.

In order that the invention fully may be understood a practical embodiment will now be described in conjunction with the accompanying drawing in Which Figure 1 is a fragmentary sectional plan of those portions of a tuner of the type specied that are necessary for an understanding of the present invention, Figure 2 being a fragmentary View of portions of Figure l showing essential parts in an adjusted position While Figure 3 is a semi-sectional end View illustrating a detail of construction, the section being taken on lines of Fig. 2.

In this embodiment, intermediate grounding or earthing of the short-circuited portion of an inductance device of the type specied above is eiected by means of an additional or auxiliary grounding contact Wheel mounted for slidable and rotary movement on the electrically grounded conducting rod 5 which also carries the usual contact Wheel provided for varying the eective inductance value of the inductance coil l, said additional contact Wheel 4 lbeing n'iaintained out electrical contact With coil l until the inductance varying Wheel S has reduced the effective inm ductanoe value of said Coil to an appreciable extent.

When the inductance value has been reduced to a predetermined value, the additional contact wheel 4 is automatically brought into mesh with the coil helix 'l to advance therealong in step with the inductance varying Wheel 6.,

The above-stated automatic meshing is effected by means of a transfer device comprising a pair of spaced pivoted arms 8, S pivoted to the coil support frame at I4 and coupled for parallel movement by means of link Ill the free end of each arm being bifurcated and located in the axially disposed path traversed by the peripheries of contact Wheels A and E.

The outermost arrn 9 of the pair of pivoted arms is located so that, in idle position, the inner branch sa of its bifurcated end holds the additional contact Wheel 4 clear of the circular path traversed lby the grounded beginning of the helically Wound incluctance coil 1, and against a light helical compression spring i! Wound about the rod 5 on which said contact Wheels are mounted,

Assuming that the inductance 'l is adjusted at or near maximum value (see Figure 2), if the coil is now rotated by any suitable means, not shown, as to cause the inductance varying contact wheel to travel in a direction to reduce said value, when said wheel reaches the inner arm it of the pair of pivoted arms, the branch 8a of the bifurcation in the free end of said arm 8 Will then be engaged by said wheel 5 and said arm, through the linkage l, will cause the outer arm 9 to advance the additional contact wheel 4 for pick up by or meshing with the coil l and continued rotation of the latter in the same direction will now cause the two contact wheels to advance in step towards the low inductance or remote end of the coil.

It is to be understood that, when travel of said wheels has moved the pair of pivoted links 9 past dead center into reverse position, (i. e. from the Figure 2 position to the Figure 1 position), the branches 8a, 9a of the bifurcations in arms 8, 9 will be out of the line of travel of said wheels which latter are then free to travel in unison towards the low inductance end of the coil. On reversing the directio-n of rotation of the coil l, to increase its effective inductance value, the pair of arms 8, 9 eventually again will be picked up by said contact wheels E and returned to the idle setting of Figure 2 by which time the said outermost arm once more will maintain the additional contact wheel d out of engagement with the turns of the coil l.

A suitable spring i2 resiliently couples the coupling link iii with the frame member lli, to which arms 8, 9 are pivoted resiliently to maintain said linked arms at the limit of permitted angular movement on either side of dead center.

Shaft 5 is maintained at ground or equivalent potential by any suitable means such as a spring i5, retained to the frame member i@ by a screw iii and connected to ground at Il.

Having now fully described and ascertained our said invention and the manner in which it is to be performed, we declare that what we claim is:

l. A variable inductance device comprising a helical spaced wound coil, means for rotating said coil, means for making variable contacts with said coil, said means including a plurality of spaced movable contact members, a conductive support for spacing said movable contact members located outside of said coil, a pair of pivoted arms linked for synchronous parallel movement on said conductive support, whereby the contact members are spaced and the coil is electrically broken into components of resonance which will not counteract the resonant characteristics of th effective portion of said coil. l

2. A variable inductance device comprising a helical spaced wound coil, means for rotating said coil, means for making variable contacts with said coil, said means including an auxiliary grounding contact wheel, a transier device including a pair of pivoted arms linked for synchronous parallel movement, a conductive support for said auxiliary grounding contact wheel located outside said coil, and means to couple said pivoted arms with said auxiliary grounding contact Wheel, whereby the coil is electrically broken into components of resonance which will not counteract the resonance characteristic of the effective portion of said coil.

3. A variable inductance device comprising a helical spaced wound coil mounted or rotation, means I" or making variable electrical contacts with said coil, said means including two electrical contacts located outside of said coil, two pivoted arms for securing said electrical contacts, a link for joining said arms together in a position which will cause said contacts to engage said coil and also electrically ground a portion of said coil when it is rotated to a predetermined position,

4.-. A device usable with a variable inductance in the form of a spaced wound helical coil mounted for rotation, said device comprising a contact support member located outside said coil, a pair of contact members mounted on said support member in a position to make contact on portions of said coil, a pair of pivoted arms positioned above said contact members and being arranged to engage said contact members and also electricalll7 ground a portion of said coil when it is rotated to a predetermined position.

REGINALD FRANCS JOSEPH FLOOD. REGNALD CECIL VINE.

REFERENCES CT'ED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,818,316 Gebhard Aug. 11, 1931 2,163,647 Ware June 27, 1939 

